Resonance is the tendency of a system to oscillate with greater amplitude at some frequencies as compared to other frequencies. The frequencies that produce maximum or larger increases in amplitude than other frequencies can be referred to as resonant frequencies or resonance frequencies. Even a small periodic driving force at a resonant frequency can result in large amplitude oscillations by the system. Different systems have different resonant frequencies, depending on material compositions, sizes, and shapes of the systems.
Vehicle systems, like other systems, have resonant frequencies. As a vehicle system travels, driving forces may cause the vehicle system to oscillate up and down and/or side to side at a resonant frequency associated with a suspension system of the vehicle system. The periodic driving forces that stimulate the oscillations may be, for example, vibrations from a motor on the vehicle system or normal forces exerted by bumps, hills, or other curves in the route. If the vehicle system travels at a certain speed, the periodic driving forces may excite the vehicle system at the resonant frequency, producing large amplitude oscillations of the vehicle system as the vehicle system travels, which may be destructive.
In a rail vehicle context, oscillations of the rail vehicle at a destructive resonance condition may damage and/or derail the rail vehicle. For example, the oscillations may bend and/or buckle structural components of the rail vehicle. The rail vehicle may oscillate with such force that the rail vehicle essentially “hops” off of the rail. Due to the nature of resonance, the track curves that drive such destructive oscillations may be fully compliant with regulations and standards, such that the slopes, curves, and undulations of the track are not in violation of such regulations and standards. Thus, the destruction caused by resonance is not necessarily mitigated by bringing sections of track into compliance with existing regulations and standards.